The present invention relates to a wrist of an industrial robot of the known type comprising:
a first wrist element, carried by a robot arm which is rotatable around a first axis with respect to a structure supporting said arm, PA1 a second wrist element, rotatably supported by said first wrist element around a second axis which crosses the first axis at an angle relative thereto, PA1 a third wrist element rotatably supported by said second wrist element around a third axis which is inclined with respect to the second axis and coplanar with said first and second axes, said third wrist element including a flange for coupling of a tool, PA1 wherein said robot arm is hollow and the second and third wrist elements are connected in rotation to two tubular shafts arranged concentrically within the robot arm, the ends of said arm and said tubular shafts opposite to the robot wrist being connected to respective motors driving rotation of said three wrist elements, PA1 said wrist elements and said tubular shafts leaving a space inside thereof free for passage of electric and fluid supply lines for the tool which is to be coupled to the robot wrist.
A robot wrist of the above indicated type is disclosed for example in U.S. Pat. No. 4,151,390.
The above mentioned known solution is particularly advantageous since it provides the arrangement of the cables for electric and fluid supply to the tool completely inside the arm and the robot wrist. However, a drawback of this solution lies in that it requires providing a tool coupling flange on said third wrist element of the robot which cannot be of a standardized type, since it must allow for passage of the tool supply lines. In case for example the tool is an electric spot welding head, these lines comprise the cables for power electric supply to the welding electrodes, the electric cables for transmitting signals emitted by sensor devices associated with the welding head, the tubes for supplying pressurized air to the welding head actuator (or electric cables in case of a head actuated by an electric motor) and the cables for supplying cooling water to the electrodes.